Well pump gas and sand control filter



Jan. 12, 1954 N. c. WELLS WELL PUMP GAS AND SAND CONTROL FILTER FiledJan. 25, 1952 i J l i PVLL s, I N V EN TOR rrQQ/VEY.

Patented Jan. 12, 1954 WELL PUMP GAS AND SAND CONTROL FILTER Norman C.Wells, Long Beach, Calif., assignor to Agate Corporation, Los Angeles,Calif., a, corporation of California Application January 25, 1952,Serial No. 268,259

17 Claims.

This invention relates to improved well pump filter attachments forcontrolling the flow of materials carried in the well liquid flowingtoward a pump. More specifically, the present devices may be capable ofeither or both separating gases from the well liquid, or controlling therate at which sand or other solids carried in the liquid Dass to thepump. Certain features of the present iilters have been shown andclaimed in patent No. 2,525,897 issued to Haskell M. Greene on Well PipeFilters, as well as in application Ser. No. 207,627 on Well Pump FilterAttachments, led January 24, 1951 by Mr. Greene, and in my copendingapplication Ser. No. 268,258 on Well Pump Filters, of even dateherewith.

The lters contemplated by this invention are of a type comprising a,body connectable to the lower suction end of a well pump, and lter meanscontained within a chamber in the body in the path of fluid flowing tothe pump. For discharging the well liquid from the lter chamber to thepump, the device includes a liquid outlet tube extending downwardly intothe filter chamber from its upper end and containing a passage leadingupwardly to the pump.

The present invention is concerned particularly 'with certain structuralimprovements in devices 4of the above character, which improvements have'proven of considerable importance in assuring a most eiective iilteringaction. For one thing, l have attained maximum freedom of fluid flow'through the filter chamber by a unique positionfing of the liquidoutlet tube, in a manner minimizing interference by the tube with thefluid flow. Specifically, it has been found desirable to position theliquid outlet tube in the chamber at a location offset horizontally fromthe center of the chamber. Preferably, the tube is positioned directlyagainst and extends vertically along a side of the chamber, to thus forma relatively wide iluid flow area between the tube and an opposite sideof the chamber.

In certain of the disclosures of the above mentioned patent andapplications, the ltering material which is employed comprises a mobilemass of interengaging lter particles, preferably glass spheres, adaptedto be displaced upwardly within the filter chamber by each surge of wellfluid toward the pump. When such movable lter materials ,are employed,the above discussed oiset -positioning of the liquid outlet tube becomeses- '.pecially important, since it increases the freedom fof movement ofnot only the well fluid, but also 'xthe upwardly moving iilter particlesor spheres.

lIn .the devices of Greene application Ser.. No.

207,627, the well fluid and filter particles, as they move upwardlywithin the chamber, are directed in a highly effective circular orupwardly spiraling course of ilow. When an offset liquid outlet tube isused in such devices, additional advantages can be obtained by speciallyforming the tube to take liquid from only a, predetermined relativelyundisturbed area of the chamber. Specifically, the tube may be designedto receive liquid from only a side thereof located downstream withrespect to the circular course of the spiralling materials. Suchformation of the tube aids especially in preventing the carryover ofgases into the pump with the well liquid.

A further object of the invention is to provide means in the filterdevice for assuring effective priming of the well pump with liquid uponeach of its suction or up strokes. This result is achieved by theemployment in the liquid outlet tube of a check valve acting to preventdownflow of fluid from the tube during the pump downstroke, and thusmaintain a charge of liquid in the pump suction line at all times. Atthe same time, I may provide means for by-passing liquid about thischeck valve and downwardly from the production string of tubing to theoutside of the filter body upon unseating of the pump within the stringpreparatory to raising of the string.

In my copending application Ser. No. 268,258, I have disclosed andclaimed means for continuously maintaining a liquid seal in a gasseparator of the present type, acting to prevent the flow of any of theseparated gases to the pump. Preferably, the devices of the presentinvention include this unique liquid sealing feature, in combinationwith those discussed above.

The above and other features of the present invention will be betterunderstood from the following detailed description of the typicalembodiment illustrated in the accompanying drawing, in which:

Figs. 1a and 1b comprise together a vertical sectional view through awell pump filter attachment embodying the invention, Fig. lb being alower continuation of Fig. la;

Fig. 2 is an enlarged horizontal section through the upper fluiddischarging head of the device, taken on line 2--2 of Fig. l;

Fig. 3 is an enlarged horizontal section taken on line 3--3 of Fig. 1;

Fig. 4 is an enlarged fragmentary vertical section through the liquidoutlet tube and its contained check valve;

Fig. 5 is an enlarged fragmentary vertical section taken on line 5 5 ofFig. 2; and

' those irregularities.

Fig. 6 is a horizontal section through the lower inlet portion of thedevice, taken on line 6--8 of Fig. 1b.

Referring first to Fig. l, a preferred form of filter Ill embodying theinvention is there shown connected to the lower end of a productionstring III) containing a conventional well pump II. The pump, which isonly partially illustrated, seats downwardly against an annular seat IIwithin the string III?, and includes the usual vertically reciprocatingpiston I2, and a lower fluid inlet check Valve I3. The pump and lterdevice are shown positioned within a well casing I4, containingperforations I through which well fluid may ilow from the formationsurrounding the casing into the well. The casing I4 normally contains ahydrostatic column of the well liquid extending upwardly to a locationhigh above the pump. c

The filter device I0 includes a tubular Vertically extending main bodysection I6, which serves as the side wall of an inner filter chamber I1,containing the lter mass I8. The lower end of chamber Il is defined by abottom wall or partition I9 extending transversely across main bodysection I5; and the upper end'of the chamber is dened by an upper head2l), threadedly connected to bodyV section I6 at 2|, and to the pump at22. Liquid and gaseous well fluid enters the lower portion of the lterchamber through side and bottom inlets 23 and 24. After the separationof liquid and gas within the chamber, the liquid leaves the chamberthrough outlet tube 25 leading to the pump, and the separated gases aredischarged to the exterior of the nlter body past check valves 26 inhead 26.

Side inlets 23 are formed as a number of vertically elongated circularlyspaced fluid passing slots in the lower portion of tubular body sectionI6. Bottom inlets 24 comprise a number of circularly spaced slots formedin, and extending radially outwardly from near the center of, chamberbottom wall I9. The inlets 23 and 24 all extend angularly through thechamber walls in which they are formed, to direct the incoming Wellfluid generally tangentially into chamber Il, and cause a circular andupwardly spiraling motion of the well uid in the chamber.

AI find itrdesirable to connect to the lower'end ofthe lter body i6 abottom fluid inlet member 40, acting to impart to the nuid moving towardinlets 24 an initial swirling motion, and to effect a separation of someof the sand from the fluid prior to entry of the fluid into the filterchamber. `extends vertically from an upper end 4I threadedly connectedto body it, to an open lower end 42. The lower end d2 of member 40 ispreferably cut on" angularly, that is, in a plane inclined to thehorizontal. edge portion of member 40 may be curved inwardly, as shownat 43 in Fig. 1b, to present a rounded surface adapted to movedownwardly past irregularities on the well casing, as the tool islowered into a well, without being caught on The side wall of tubularmember 4D contains a number of vertically elongated inlet slots 44,through which fluid enters member 40 for passage upwardly into the nlterchamber. Slots 4I! extend angularly orV generally tangentially throughthe wall of member 4) (see 6), to direct the incoming fluid in anupwardly spiraling course of now as it moves toward the lter chamber.Inlets' 44 direct fluid inthe same circular direction as the `filtercham- This member 40 is tubular as shown, and

The bottom ber inlets 23 and 24, and thus increase the spiraling motionwithin the lter chamber. Also, the spiraling motion of the fluid withinmember 4l acts to eifect an initial separation of some of the sand fromthe fluid, to fall downwardly through the open lower end 42 of member130 and back into the well. It is contemplated that when inlet member 40is connected to the lower end of the lter body, the side inlets 23 tothe lter chamber may be eliminated, so that all fluid flowing to thefilter chamber must pass through the inlet member.

The filter material I8 is initially received within the lower portion ofchamber I1, and comprises a mobile and vertically displaceable mass ofdiscrete and interengaging filter particles. For best results, thesefilter particles should take the form of glass spheres, preferably of adiameter between about -binch and 1/2 inch. Upon each upstroke of thepump piston, the resulting circular and upwardly spiraling ow of welluid within chamber l1 causes a correspending circular and upwardlyspiraling motion'r of the filter particles or spheres, as well as aspinning motion of the spheres about their in-4 dividual axes. Suchupward spiraling motion of the spheres is limited by their engagementwith a perforated transverse partition 2l received between liquid outlettube 25 and chamber side wall I6 at a location spaced beneath the top ofthe chamber.

As the well uid flows upwardly through the filter mass I8, contact ofthe fluid with the lter particles causes separation of the gases fromthe Well liquid, which separation is greatly enhanced by the violentspiraling and spinning motions of the particles. At the same time, thefilter mass acts to control the amounts of sand and other entrainedparticles flowing to the pump with the well liquid. More particularly,the filter mass prevents passage to the pump at any time of suddencharges of sand or the like in quantities suiicient to materially damagethe pump, butV instead passes these solid materials to the pump at arelatively uniform and safe rate. When the flow of solid particles isthus regularized, these particles can be maintained in suspension withthe Well liquid during their en-l tireA passage through the pump, andthe usual damage to the pump is avoided.

The liquid discharge tube 25 isthreadedly con-v nected to the undersideof head 20 at 28, and communicates with passage 29'in the head leadingupwardly to the pump. Tube 25 projects downwardly into chamber I'I,V andterminates in a tapered and closed lower end 30 located a short distanceabove the lter mass in its condition of repose. In order to provide aliquid and lter particle now area of maximum horizontal dimension at oneside of tube 25, the tube is positioned at a location offsethorizontally from the center of chamber Il. Preferably, tube 25 islocated directly against a side ofthe chamber, so that the upwardlyspiraling iiuid and filter particles may follow the extended andrelatively free course represented by the arrows 3l in Fig. 3.

The well liquid enters liquid outlet tube 25 through a number ofapertures 32 formed in the Wall of the tube. 'Iheuppermost of theseapertures is spaced a substantial distance below the gas outlet valves26, so Vthat the mperforate upper portion of' tube 25 forms with head 36and main body section I6 an enclosed upper gas receiving space. v

In order to. minimize the chances that any gases will now with theliquid into the liquid outlet tube, the apertures 32 in that tube are sopositioned as to take liquid from only the most calm and undisturbedportion of the chamber Il. Specically, these apertures are located at aside of tube 25 which is downstream with respect to the circular courseof fluid and filter particle flow within the chamber. Preferably, theseapertures are formed in only the most removed portion of even thatdownstream side of the tube, specically in an approximately 90 portionthereof nearest the body side wall and designated at a in Fig. 3. i

To assure the delivery of a relatively dead body of liquid to the pumpupon each upstroke, I preferably connect into the liquid outlet tube 25a check valve unit 33. 'Ihis unit includes a ball check valve element 34adapted to pass liquid upwardly to the pump during its upstroke, but toprevent the downward iiow or any of the liquid during the pumpdownstroke. For best results, the check valve unit should be connectedinto the outlet tube at a location directly above the uppermost tubeaperture 32.

The separated gases escape from the upper portion of the chamber througha number of passages 35 in the head, each of which extends rst upwardlyfrom the top of the chamber and then laterally to the outside of thedevice. There may typically be seven of these passages, at locationsspaced about a semi-circular extent of the head opposite the portion ofthe head from which liquid outlet tube 25 depends. A check valve 26 ispositioned within the upwardly extending portion of each passage 35, toprevent reverse or inward fluid flow, and to regulate the outward flow.

Predetermination of the degree of loading of check valves 26, preferablyby merely controlling their weights and their areas subjected topressure, is of considerable importance in assuring most eiective gasseparation in the present device. For one thing, these check valvesshould be so designed as to resist opening movement to an extent at alltimes maintaining a body of unexpelled gas in the upper portion of thechamber. The presence of Such a gas column above the liquid creates aliquid-gas interface in the chamber, which in accordance with knownprinciples encourages a continuing separation of gas from the liquid.

The loading of check valves 25 is important also for controlling theliquid level within the ilter chamber, in a manner preventing dischargeof any gases to the pump with the well liquid. Specifically, the checkvalves should be loaded sufficiently lightly to under all circumstancesmaintain the liquid level in the chamber above the uppermost one of theliquid outlet apertures 32. In this way, a highly effective liquid sealis provided at the liquid outlets, positively preventing access of anyof the separated gases to those outlets.

With specific reference to the manner in which check valves 26 controlthe liquid level in the chamber, it is noted that as gases accumulate inthe upper portion of the chamber an unbalanced condition is set upbetween the hydrostatic columns at the inside and outside of the filterbody. This unbalanced condition evidences itself in the exertion of adifferential pressure tending to open check Valves 2B. As will beunderstood, this differential pressure is caused by the weight of an`unbalanced portion of the outer liquid column horizontally opposite andcorresponding in height the pump seat. In the to the inner gas column.Thevalue of this differential pressure exerted against the valve may becalculated for any particular height of gas column from the followingformula, assuming the weight of the inner gas column to be negligible:

=H D Where,

P=differential pressure in lbs. :height of gas column in feet. D=densityof iluid in outer fluid column in lbs. per square inch per ft. of heightof fluid column.

per square inch.

Where L=minimum permissible distance X in inches from uppermost liquiddischarge aperture 32 to gas outlet valve seat.

D=density of lightest uid likely to be encountered in annulus outside oflter body, in lbs. per sq. in. per ft. This lightest density likely tobe encountered is about 0.06 lb. per sq. in. per ft., the density of oiland gas froth. The heaviest fluid encountered is salt water which has adensity of about .46 lb. per sq. in. per ft.

In a typical filter device which has proven extremely effective in verygassy wells, the various parts have the following proportions andcharacteristics:

1. Chamber diameter-:41/2.

2. Vertical distance X between seats of gas escape check valves 26 anduppermost liquid outlet aperture=38.

3. Vertical distance between check valves 26 and liquid level at whichcheck valves are opened by hydrostatic pressure-:4%

4. Pressure at which check valves open=l6 lb./sq. in.

When the production string l0 is for any reason to be removed from thewell, it is desirable to provide means for draining the Well fluidcontained Within the string from its lower end. For this purpose, it iscustomary to first lift the pump Il from its seat I |I,` and preferablyremove it completely from the string, so that the fluid may owdownwardly from Within the string and past present device, however,ycheck valve 34 within liquid outlet tube 25 prevents downward drainageof the fluid through that tube and the filter chamber. Consequently, Ifind it desirable to provide means for passing liquidfrom the liquidpassage about valve 34 directly to the outside 0f the tool body, duringremoval of the production string and filter device from a well. For thispurpose, head 2l! of the filter body may `contain an upwardly andoutwardly extending passage 35a, formed the same rasthe :seven gasescape! passages v35 but :com- 4nninic'ating with liquidoutlet passage29 rather V4,than the .lter chamber. To effect such corn- ;municationwith liquid passage 29, a duct i5 may vbe formed in head leading fromthat passage to the upwardly extending portion of passage a. Beneath thepoint of communication with duct 45, passage 35a may be closed olf by abottom plug 46, to prevent the upward ilow of gases from the filterchamber into that passage. Above its point of communication with duct45, passage 35a contains a valve seat 26h, on which a dischargecontrolling ball valve 26o seats downwardly. A second ball 26d may reston the valve 26C, so that the opening pressure of valve 2te is greaterthan the opening pressures of gas outlet valves 26. As will beappreciated, upon elevation of pump II within the production string to apoint at which liquid may flow downwardly with- .in the string and pastthe pump, liquid flows downwardly within passage 29 and head 2i), thenthrough duct and passage 35a, and past check Valve 2Go to the exteriorof the iilter body. In this manner, liquid is drained from the lowerportion of the production string, to facilitate removal of the stringfrom the well.

n the operation of the illustrated apparatus, the pump piston isreciprocated in the usual manner, to cause intermittent surges of liquidand gaseous well fluid upwardly into the filter chamber and toward thepump. Inlets 2li and 25 direct the incoming fluid in upwardly spiralingpaths within the chamber, to cause a corresponding upwardly spirallingmotion of the filter spheres. Passage of the fluid through the Vspheremass separates the gases from the well liquid, and regularizes the flowof sand to the pump. The separated gases rise upwardly for dischargepast check valves 26, which function in the manner previously discussedto maintain both a gas column in the chamber and a liquid seal at theliquid outlets. The relatively gas-free liquid flows into tube 25 and tothe pump.

Iclaim:

l. A Well pump filter device comprising a tubular body containing avertically extending charnber and adapted torbe carried beneath a wellpump, means forming an inlet admittingV well fluid into the chamber,lter means in the path of iiuid flow through the chamber, said filtermeans comprising a mobile and vertically displaceable mass ofinterengaging filter particles, and a liquid outlet tube extendingdownwardly within the chamber at a location horizontally oilset from thecenter thereof and containing a liquid outlet passage leading upwardlyfrom the chamber to the pump.

Y 2. A well pump filter device comprising a tubular body containing avertically extending chamber and adapted to be carried beneath a wellpump, Vmeans .forming an inletdirecting well fluid in a circular coursewithin said chamber, lter means in the path of iluid flow through thechamber, and a liquid outlet tube extending downwardly within thechamber at a location horizontally offset from the center thereof andcontaining a liquid outlet passage leading upwardly from the chamber tothe pump, the wall of said tube having aperture means leading into isaidlpassage at .aside of the tube downstream opposite upstream side.

3. A well pump lter device comprising a tubular body containing avertically extending chamber and adapted to be carried beneath a wellpump, means Vforming an inlet admittingwell fluid into the chamber,filter means in the path of fluid ilow through the chamber, said filtermeans comprising a mobile and vertically displaceable mass ofinterengaging filter particles, and a liquid outlet tube extendingdownwardly within the chamber at a location horizontally offset from thecenter of the chamber and against a side wall thereof and containing aliquid outlet passage leading upwardly from the chamber to the pump.

4. A well pump iilter device comprising a tubular body containing avertically extending 'chamber and adapted to be carried beneath 'a wellpump, means forming an inlet admitting liquid and gaseous well iiuidinto the chamber, a mobile and vertically displaceable mass ofinterengaging lter particles in the path of fluid iiow through thechamber acting to separate gases from the well liquid, a liquid outlettube extending downwardly within the chamber at a location horizontallyoiset from the center thereof and containing a liquid outlet passageleading upwardly from the chamber to the pump, and means forming anescape from the upper portion of the chamber to the exterior of thebody.

5. A well pump filter device comprising a tubular body containing avertically extending chamber and adapted to be carried beneath a wellpump, means forming an inlet admitting liquid and gaseous well fluidint-o the chamber, a mobile and vertically displaceable mass ofinterengaging filter particles in the path of iiuid flow through thechamber acting to separate gases from the well liquid and control sandflow through the chamber, and a liquid outlet tube extending downwardlywithin the chamber at a location horizontally oifset from the center ofthe chamber and near a side wall thereof and containing a liquid outletpassage leading upwardly from the chamber to the pump, said chamberhaving upper gas outlet means, and check valve means preventing uidinflow through said outlet means.

6. well pump filter device comprising a tubular body containing avertically extending chamber and adapted to be carried beneath a wellpump, said body containing an inlet admitting liquid and gaseous welluid into a lower portion of the chamber, a mobile verticallydisplaceable mass of interengaging ilter particles in the path of fluidow through the chamber and acting to separate gases from the well liquidand control sand passage through the chamber, a liquid outlet tubeprojecting downwardly into said chamber at a location horizontally oisetfrom its center and adjacent a side wall thereof, said tube containing aliquid discharge passage leading to said pump and communicating with thechamber at a predetermined location spaced below the top of the chamber,the wall of said tube being imperforate above said location, gas outletmeans for separately discharging gases from an upper portion ci thechamber above said location to the outside of the body, and check valvelmeans preventing fluid inflow through said outlet means and resistingthe gas discharge to maintain a body of gas in the chamber above theliquid, said check valve means being loaded suiliciently lightly tomaintain the liquid level Yin the chamber at all times above saidlocation,

7. A well pump filter device comprising a tubular body containing avertically extending chamber and adapted to be carried beneath a wellpump, means forming an inlet admitting well passage at a locationbeneath theptop of said* chamber and preventing fluid downflow throughsaid i passage.

8. A well pump lter device comprisinga tubu lar body containing avertically extending chamber and adaptedrto `bejcarried beneath a wellpump, meansforming an inlet admitting liquid and-gaseous wellfluidfintothe chamber, means in the path `of fluid flow throughthejchainberactingto separate gases from the well liquid, a liquid outlet tubeextending downwardly within the chamber and containinga liquid outlet`passage leading upwardlyfromthe chamber to the pump, means forminganescape passage for discharging the separated gases from an upperportion of the chamber to the exterior of thebody, and a check valve`contained in said liquid outlet passage at a locationbeneath the top ofsaid chamber and preventing iluid downilow through said passage.

9. A well pump iilter device comprising a tubular body containing avertically extending chamber and adapted to be carried beneath a wellpump, means forming an inlet admitting liquid and gaseous well iiuidinto the chamber, a mobile and vertically displaceable mass ofinterengag ing iilter particles in the path of fluid flow through thechamber acting to separate gases from the well liquid and control sandow through the chamber, a liquid outlet tube extending downwardly withinthe chamber and containing a liquid outlet passage leading upwardhr fromthe chamber to the pump, said chamber having upper gas outlet means,check valve means preventing fluid inflow through said outlet means, anda check valve in said liquid outlet passage below the top of the chamberpreventing fluid downilow through the passage.

, 10. A well pump lter device comprising a tubuvlar body containing avertically extending chamber and adapted to be carried beneath a wellpump, means forming an inlet admitting well fluid into the chamber,filter means in the path of fluid flow through the chamber, said filtermeans comprising a mobile and vertically displaceable mass ofinterengaging lter particles, a liquid outlet tube extending downwardlywithin the chamber at a location horizontally offset from its center andadjacent a side wall thereof and containing a liquid outlet passageleading upwardly from the chamber to the pump, and a check valve in thebody within said liquid outlet passage preventing fluid downflow throughthe passage.

1l. A well pump lter device comprising a tubular body containing avertically extending chamber and adapted to be carried beneath a wellpump, said body containing an inlet directing liquid and gaseous wellfluid in a circular and upwardly spiraling course within said chamber, amobile and vertically displaceable mass of inter-engaging sphericaliilter particles in the path of fluid iiow through the chamber andacting to separate gases from the well liquid and control sand passagethrough the chamber, a liquid outlet tube projecting downwardly intosaid chamber at a location horizontally offset from its center andadjacent a side wall thereof, said tube terminating downwardly in aclosed lower end i `1o positioned abovethe particle mass `in its condi--tion of repose, said tube containing a liquid discharge passage leadingto said pump and communicating with the chamber through aperture meansin the tube wall positioned below the 'top of the chamber andat a sideof the tube downstream with respect to the circular course of iiuidiiow, the Wall of said tube being imperforate above said location and atits upstream side, gas outlet means `for separately discharging gasesfrom an upper portion of the chamber above said location to the outsideof the body, check valv'e means preventing fluid inflow through saidoutlet means and resisting the gas discharge to maincheck valve in saidliquidoutlet tube ata loca-"' tion substantially directly above saidaperture means and `preventing downward iluid ilow through the tube. i

12. A well pump filter device comprising a tubular body containing avertically extending chamber and adapted to be carried beneath a wellpump, means forming an inlet directing Well iiuid in a circular coursewithin said chamber, filter means in the path of fluid llow through thechamber, and a liquid outlet tube extending downwardly within thechamber at a location horizontally offset from the center thereof andcontaining a liquid outlet passage leading upwardly from the chamber tothe pump, the wall of said tube having aperture means leading into saidpassage at a side of the tube downstream with respect to the circularcourse of fluid flow, said aperture means being formed in only anapproxi mately degree portion nearest the body wall of said downstreamside of the tube.

13. A well pump filter device comprising a tubular body containing avertically extending chamber and adapted to be carried beneath a wellpump, means forming an inlet admitting liquid and gaseous Well iiuidinto the chamber, means in the path of fluid flow through the chamberacting to separate gases from the well liquid, a liquid outlet tubeextending downwardly Within the chamber and containing a liquiddischarge passage leading to the pump and communicating with the chamberthrough aperture means in the tube wall positioned below the top of thechamber, a check valve in said liquid outlet tube at a locationsubstantially directly above said aperture means and ybelow the top ofsaid chamber preventing downward iiuid flow through the tube, and meansforming an escape passage for discharging the separated gases from anupper portion of the chamber to the exterior of the body.

14. A well pump filter device comprising a tubular body containing avertically extending chamber and adapted for attachment to the lower endof a production string within which a well pump is seated, means formingan inlet admitting well fluid into the chamber, iilter means in the pathof fluid iiow through the chamber, a liquid outlet tube extendingdownwardly within the chamber and containing a liquid outlet passageleading upwardly from the chamber to the pump, a check valve in saidliquid outlet passage preventing iluid doWni-low therethrough, meansforming a passage leading from a portion of said liquid outlet passageabove said check valve to a location at the outside of said body andstring and through which liquid from within the string may drain uponunseating of said pump, and

l l check valve means resisting liquid flow from the body through'saidlast mentioned passage until a predetermined pressure is reached in saidoutlet passage and preventing reverse ow therethrough.

15. A well pump lter device comprising a tubular body containing avertically extending chamber and adapted to be carried at the lower endof a well pump, a wall carried by said body forming the bottom of saidchamber and containing inlet apertures admitting well iluid into thechamber, filter means in the path of uid flow through the chamber, aliquid outlet leading from said chamber upwardly to the pump, and a tubeprojecting downwardly from said body below said bottom wall of thechamber and containing openings in its side through which fluid entersthe tube for passage upwardly through said apertures to the chamber,said openings being disposed at an angle directing the uid in a circularand upwardly spiraling course of flow Within the tube, said tube havinga bottom opening through which materials from the fluid may falldownwardly.

16. A well pump lter device as recited in claim References Cited in thefile of this` patent UNITED STATES PATENTS NumberV Name- Date 1,192,145Williams July 25, 1916 1,478,427 Dulaney Dec. 25, 1923 1,620,347 Hawkinset al Mar. 8, 1927 1,628,900 Nielsen May 17, 1927 2,517,198 Gilbert Aug.1, 1950 2,525,897 Greene Oct. 17, 1950

